Heat treatable titanium base alloys and method



United States Patent 3,405,016 HEAT TREATABLE TITANIUM BASE ALLOYS AND METHOD Robert I. Jatfee, Worthington, and Horace R. Ogden, Columbus, Ohio, assignors, by mesne assignments, to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New Jersey No Drawing. Confinuation-in-part of application Ser.

' No. 520,357, July '6, 1955. This application Apr. 11,

1956, Ser. No. 577,461

' 3 Claims. (Cl. 148-133) This invention pertains to titanium-base alloys of novel composition and proportions, which are .heat treatable by quenching for imparting relatively low yield strengths to facilitate forming operations, and which may thereafter be strengthened by cold working and aging or precipitation hardening. The invention also pertains to methods of heat treating such alloys for imparting the properties aforesaid.

This application is a continuation-in-part of our cpending application Ser. No. 520,357, filed July 6, 1955, now abandoned which 'is in turn a continu'a'tion-in-part of our applications Ser. Nos. 122,576, filed Oct. 20, 1949, now Patent No. 2,726,954; 305,284, filed Aug. 19, 1952, now Patent No. 2,798,806; 392,052, filed Nov. 13, 1953, now abandoned; 393,578, filedNov. 23, 1953, now Patent No. 2,796,347; 396,756, filed Dec. 7, 1953, now Patent No. 2,797,996; 400,730, filed Dec. 28, 1953, now aban doned; 400,744, filed Dec. 28, 1953, now Patent No. 2,779,677; 409,252, filed Feb. 9, 1954, now abandoned, and 470,510 filed Nov. 22, 1954, now abandoned.

There are many applications in which a large spread between yield strength and utimate strength is desirable in an alloy. For example, when alloys are to be plastically formed to shapes, as by forging, rolling, extruding, drawing, etc., it is desirable to have a low yield strength so that the forming operation can be accomplished more easily. Also, it is desirable to strengthen the alloy after forming by a simple aging heat treatment.

We have discovered that there is a certain class of titanium-base alloys that can be heat treated to produce low yield strengths before forming. These are alloys 3,405,016 Patented Oct. 8, 1968 which contain both substitutional alpha stabilizers and beta stabilizers, the betaastabilizer content being less than the critical amount required to produce mechanically stable beta phase on quenching from the a1l-beta temperature field. There are certain composition limits which must be met before the desired properties are obtained. Also, it is necessary to use a prescribed heat treatment to have the alloys in the correct condition to display this low-yield-strength, high-ultim-ate-strength property. The alloys of the present invention when'quenched from the all-beta and mixed alpha-beta temperature field produce a yield strength to ultimate tensile strength ratio of between about 0.25 and 0.75.

In most beta-stabilized, titanium-alloy systems, there is a composition range in which the beta phase transforms to martensite when the alloy is quenched from the allbeta temperature field. At alloy contents just above this range, the beta phase can be retained by quenching. This beta phase is, however, unstable, and, in most systems, it is hardened by the formation of a coherent precipitate during the quenching precess. It has been found that the addition of an alpha stabilizer, such as aluminum, tin or antimony, to alloys containing this beta-stabilizer content, prevents the formation of the coherent precipitate during the quench. The resultant alloy as quenched from the beta temperature field, has a soft beta structure, a very low yield strength, a high ultimate strength and good bend ductility. The beta structure will transform to martensite on cold working, or it can be age hardened to high strength levels.

The compositional limits of the soft beta phase-having the large spread between yield strength and ultimate strength will vary according to the beta-stabilizing elements used. It has already been stated that the alloy must contain a substitutional alpha stabilizer in addition to the beta stabilizer. The alpha-stabilizer content may range from 1 to 10% for aluminum, 1 to 23% for tin, or 1 to 19% for antimony, or combinations thereof, tin being replaceable by antimony, and vice versa on a substantially equal percentage basis, and antimony and tin being substitutable for aluminum in the proportion of about 3% of tin and/or antimony for 1% of aluminum. The beta-stabilizer content for alloys quenched from'the TABLE ire-MECHANICAL PROPERTIES OF BETA-QUENCHED 'II-BASE ALLOYS p.s.i.X1,000

-- Percent Composition Heat Treatment 1 Percent Alloy N Percent, 0.2% Elongation Red. in MBR, T VHN Balance Ti Time, Temp, Ofi'set Ult. Str. in 1 Area (Long) hr. 0. Yield Str.

' A-478 L 5 111-4 M0; 1 950 133 150 2 4 B1 383 9 Sn-IO Cr- 1 850 129 130 16 31 0.9 330 1 Quenehed from temperature.

beta field may have the following ranges or combinations thereof: to 15% molybdenum, 15 to 20% vandium, 6 to 3% manganese, 4 to chrominum, and 4 to 5% iron.

Tensile data on beta-quenched alloys, showing the large spreads between yield strengths and ultimate strengths for alloys within these limits, are given in Table I.

As shown by the above data, the most effective compositions for producing a large spread between yield and ultimate strengths are those containing about 8 to 10% molybdenum, about 7 to 8% manganese, about 7 to 8% chromium and about 4% iron.

It is not necessary to quench these alloys from th beta field to obtain the high spread between yield and ultimate strengths. Quenching from a temperature in the alpha-beta temperature field, so that the beta phase retained at room temperature has a composition within the limits described above, will produce the same effect. Examples of this effect are given in the following Table II, which contains tensile data for alloys quenched from the alpha-beta field:

quenched condition. Obviously, the beta-stabilizer content cannot exceed the maximum specified above for each alloying element; as otherwise the beta-phase composition will exceed that of the desired ranges. The minimum betastabilizer content to produce an alpha-beta structure in the quenched condition is the lower effective limit for alpha-beta-quenched alloys, producing alpha-beta alloys on quenching. This minimum limit is 1% for each of molybdenum, manganese, chromium and iron, and 2% for vanadium. Thus, this invention is applicable to alphabeta alloys having beta-stabilizer contents of 1 to 15% molybdenum, 2 to vanadium, 1 to 8% manganese, 1 to 10% chromium, and 1 to 5% iron in addition to the alpha promoters specified previously.

This heat treatment can be used on commercial heats of titanium alloys provided they have the prescribed compositions. For example, the Ti-4Al-4Mn alloy can be heat treated to have a large spread between yield and ultimate strengths by quenching from about 900 C. When quenched from this temperature, the manganese content of the beta phase is of the appropriate composi- TABLE II.MECHANICAL PROPERTIES OF TIIM ALLOYS QUENCHED FROM THE ALPHA-BETA Heat p.s.i.X1000 Composition Treatment 1 Percent Percent Alloy No. Percent 0.2% Elongation Red. in MB R,T VHN Balance Ti Time, Temp., Offset Ult. in 1' Area (Long) hr. 0. Yield Str.

5 800 105 146 6 10 7. 8 356 2 850 95 156 8 10 3. 9 352 1 2 950 106 143 10 7 4. 5 363 8 775 125 133 13 21 7. 5 .355 3 825 68 153 12 15 2. 8 309 1 2 950 96 149 10 7 B1 358 1 875 93 158 15 13 1. 6 393 2 750 66 111 15 51 0. 5 268 2 2 750 64 112 8 0.9 255 3% 975 65 113 4 4 6. 6 421 4 750 79 116 14 27 0. 8 254 4 750 68 114 17 25 0 294 4 760 94 133 16 29 1. 5 272 4 Al-IO V 4 750 66 132 10 25 1.3 259 4 111-2.5 V-2.5 Mo.-- 4 750 130 146 8 25 2. 1 328 5 Sn-5 Mo-5 V 4 750 72 109 20 38 1. 1 806 l Quenched from temperature. 2 Quenehed from the beta field.

As shown by the above data, a typical example is the Ti-5Al-5Mo alloy. When this alloy is quenched from 800 C., the molybdenum content of the beta phase is above the optimum 10%. When quenched from 850 C., the molybdenum content of the beta phase is closer to the optimum 10%, and a very low yield strength spread is obtained, the properties being very similar to an alloy of this same analysis, as quenched from the beta field, the results of which latter, copied from Table I, are repeated in Table II for comparison. Another example is the Ti-SSn-SMo alloy quenched from 750 C., which has an alpha-beta structure, the beta phase of which contains about 10% molybdenum. The properties of this alloy, as shown in Table II, are very similar to the Ti-5Sn-10Mo alloy quenched from the beta field, which, of course, has a molybdenum content of 10% in the beta phase.

Where the alloys are quenched from the alpha-beta field, it is not necessary to limit the alloy content to the ranges specified previously. For this condition, the requirements are: (1) that the quenching temperature in the alpha-beta field is in all instances selected such that the retained-beta phase has a composition within the limits above specified for the beta stabilizers, respectively, as quenched from the beta field, i.e., within 5 to 15% molybdenum, 15 to 20% vanadium, 6 to 8% manganese, 4 to 10% chromium, and 4 to 5% iron, and (2) that the alloy have a two-phase alphabeta structure in v the QUENCHED FROM VARIOUS TEMPERATUR ALPHA-BETA FIELD BS IN THE Heat Treatment l 0.2% 01Iset Ultimate Percent Percent Yrel Strength, Elongation Red. in Temp., Tune, Strength, p.s.i. in 1" Area 0. hr. p.s.i.

Heat B-5306 Heat BN-44056 7 Heat Treatment l Compressive I Yield Temp., C. Time, hr. Strength,

p.s.i.

Heat B-31399 l Quenched from temperature. 2 Brittle.

Additional test data illustrative of the above are given in the following Table IV'for molybdenum containing alloys as betal quenched, i.e., as solution treated one hour at 870 C. and water quenched.

TABLE IV. EFFECT OF SOLUTION-HEAT TREATMENT ON THE PROPERTIES OF Ti-Sn-MO Ti-Al-Mo AND Tl-Sn-Al-Mo BETA ALLOYS Tensile Properties: Elongation,

p.s.i.X1,000 Percent Composition percent (Balance Percent MBR,T Titanium) 0.2% Red. (Trans) VHN Ofiset Ultimate Total Uniform in area Yield Strength Strength 18 Sn-8 Mo 118 124 11 3 36 0.75 284 123 124 11 3 I 36 0 285 112 118 1 18 3 36 0 282 118 121 9 3 30 0 289 114 116 16 2 36 O 283 1 15 120 17 50 0 267 41 137 11 7 15 1. 1 273 117 121 18 2 45 0 290 89 124 9 8 31 1. 4 270 61 134 8 6 13 0. 45 259 117 122 14 3 37 0 275 87 119 11 10 46 0. 5 262 43 125 11 8 24 0. 9 257 74 125 14 13 19 294 94 109 14 38 0 253 38 100 20 8 49 0. 5 312 125 11 8 13 0.55 269 81 123 15 14 23 295 138 142 6 2 34 0 320 66 99 38 31 48 0 257 66 33 30 40 5. 0 260 67 127 16 16 12 9. 0 320 88 121 12 12 15 0 305 97 112 10 10 12 10 330 106 121 22 22 20 6. 6 325 72 126 A 17 A 17 26 2. 2 300 129 12 3 36 0 299 76 124 7 6 5 l. 2 289 2 A 72 118 18 1O 32 3. 4 280 4 A1 130 137 11 3 32 0 315 3 A1 125 133 13 1 35 1. 5 312 3 Al-8 125 130 12 1 35 0 292 3 141-4 Sn-12 Mo.-- 114 131 11 4 27 1. 2 300 2 111-8 Sn-8 Mo 46 145 10 7 17 1. 4 278 2.67 Al8 Sn-4 Mo-8 Cu. 116 134 13 10 21 9. 2 337 2.67 Al-8 Sn-4 Mo-6 Cu. 74 132 6 6 2O 2. 0 296 2.67 A1-8 Sn-4 Mo-4 Cu- 79 147 14 10 9 1. 5 323 2 Al-8 Sn-8 Mo-6 Cu 122 125 6 2 14 0 295 2 141-8 Sn-B Mo-4 Cu. 111 114 7 3 32 0. 9 301 2 Al-S Sn-8 Mo-2 Cu.... 91 133 10 7 26 1. 9 308 2.67 Al-8 Sn-4 M0-6 Mn. 68 150 15 11 24 3. 0 293 2.67 Al-S Sn-4 Mo-3 Mn. 71 143 10 8 6 1. 4 289 2 111-8 Sn-8 Mo-6 Mn 121 123 18 3 36 0 297 2 AH; Sn-8 Mo-3 Mn.- 87 168 11 10 4 1. 6 298 2 A18 Sit-8 M0-2 Fe-. 125 125 12 3 36 0 313 2 111-8 811-8 Mo-6 Or 121 121 19 3 34 0 309 2.67 Al.8 Sit-4 M0-8 FeCr. 135 137 7 3 1B 1. 2 333 2.67 Al-8 Sn-4 Mo-4 FeCr 113 5 3 4. 8 319 1 Average of tests from three melts.

annealing treatment prior to aging. The beta phase in this heat-treated condition is subject to precipitation hardening when heated at temperatures in the range of 300 to 550 C. Thus, an alloy within the prescribed compositional limits can be heat treated to have a low yield strength and good bend ductility by quenching from the appropriate temperature. After quenching, the alloy can be formed into shape and then aged to the desired strength level. Examples of the properties in the quenched condition and in aged conditions of some representative alloys are given in the following Table V.

TABLE V.PROPERTIES or QUENCHING AND AGED TI-BASE ALLOYS Quenching Aging Treatment p.s.l. 1000 t Treatment Percent Percent Composition, Percent (Balance Titanium) 0.2% Elongation Red. in MBR, '1 Time, Temp., Time, Temp., Ofiset Ult. Str. in 1" Area (Long) hr. 0. hr. 0. Yield Str.

4 Al-IO V (RS-523-57) 4 750 66 132 10 25 1.3 4 750 4 500 167 181 3 14 3. 2 4 750 64 500 180 186 3 13 3.

Sn-5 Mo-5 V (RS-523-62) 4 750 72 109 20 38 1.1 4 750 4 500 179 194 2 4 8. 2 4 750 64 500 154 171 8 4. 8

5 Sn-10 Mo (RS-523-39) 2 750 64 112 8 30 0.9 2 750 4 500 176 189 2 9 5. 0 2 750 64 500 176 176 5 19 2. 8

5 811-5 V (RS-523439) 4 750 79 116 14 27 0. 8 V 4 750 4 500 121 136 6 19 1. 8 4 750 64 500 111 127 9 1.7

4 111-5 V (RS-523-55) 1- 4 750 94 133 16 29 1. 5 4 750 4 '500 127 146 14 27 2. 7 4 750 64 500 133 156 11 11 2. 0

4 Al-2.5 V-2.5 Mo (RS-523434) 4 750 130 I 146 8 2.1 4 750 4 500 138 154 7 23 3. 6 4 750 64 500 147 160 5 15' 2. 5

3 811-6 Mo (RS-143948) 1 870 88 121 12 15 6 Sn-6 Mo (RS-1439-49) 1 870 81 183 15 23 1 870 16 550 172 176 2 15 9 811-6 Mo (RS-1439-) 1 870 74 125 14 19 8 Sn-10 Mo (RS-1439413) 1 870 38 20 1 870 16 540 149 165 4 10 511-10 M0 (RS-1439-34) 1 870 87 119 11 1 870 16 510 157 172 5 12 Sn-10 Mo (RS1439-35) 1 870 89 124 9 1 870 16 540 141 158 6 14 311-10 Mo (RS-1439-30) 1 870 17 50 1 870 16 510 181 190 3 14 4 Sn-12 Mo (RS-1439436) 1 870 66 99 38 48 8 Sn-12 Mo (RS-143237) 1 870 94 109 15 38 10 Sn-12 M0 (RS-1439-29) 1 870 117 122 14 1 870 16 540 144 7 1 870 32 480 156 169 4 12 Sir-12 Mo (RS-1439-28) 1 870 117 121 18 1 870 16 510 173 179 4 1 870 64 480 194 203 3 12 811-12 Mo (RS-1439-26) 1 870 114 118 17 1 870 16 590 130 134 8 1 870 64 480 168 177 2 5 Sn-15 Mo (RS-143943) 1 870 138 142 6 870 16 510 1 1 870 32 480 211 216 1 3 111-10 Sn-12 Mo (RS-1439-31) 1 870 125 133 13 1 870 16 510 204 206 3 1 870 32 540 196 200 2 1 870 32 590 161 166 7 Another ingot analyzing 5.4% aluminum, 3.4% vanadium, balance titanium of commercial purity, as water quenched from 820 C., has a 0.2% offset yield strength of 118,000 p.s.i., an ultimate strength of 142,000 p.s.i., an elongation of 16% and an area reduction of 50.5%. On subsequent aging at 890 F. for eight hours, the corresponding values were: yield strength 144,000 p.s.i., ultimate strength 163,000 p.s.i., elangation 9% and area reduction 23 The alloys of the invention are further characterized by a rapid increase in work-hardening rate during cold working. This rapid Work hardening occurs after an initial period of low work hardening: It is believed to be the results of martensite formation of alpha from beta, which is accompanied by increased hardiness and strength. Thus, the alloys can be highly wor-k hardened or strengthened. This is a fuither mechanism whereby the strength of the alloys may be increased, augmenting the aging mechanism described previously.

Summarizing the above data, it is seen that certain titanium-base alloys can be heat treated to have very low yield strengths. In this heat-treated condition, the alloys can be fabricated or formed to shape and subsequently age-or precipitation-hardened to high strength levels. The requirements for such alloys are: (1) the alloy must contain an alpha sabilizer, such as aluminum, tin and antimony, and also a beta stbilizer. The betastabilizer content cannot exceed 15% for molybdenum, 8% for manganese, 10% for chromium, 5% for iron, or 20% for vanadium, or proportionate combinations of the above. It is preferable that the beta-stabilizer content be less than the optimum to produce the largest spread between yield and ultimate strengths when quenched from the beta field. This is 10% for molybdneum, 7.5% for managanese, 7.5% for chromium, 4% for iron, or 15% for vanadium. When these alloys contain less than the optimum amount of beta-stabilizing elements, they must be quenched from a temperature 9 in the alpha-beta field at which the beta phase of the alloys alloys is of the optimum composition; (2) the heat treatment given the alloys is a' quench from the temperature at which the beta phase is a composition within the limits described above; and (3) subsequent to quenching, the alloys may be fabricated to shape and then aged to high strength levels by reheating to 300 to 550 C. sfor periods of time from a few minutes to several days.

All of the alloys, test results for which are given in Tables I to V, inclusive, were produced by are melting the alloying constituents in a cold mold furnace in an inert or argon atmosphere, The alloys thus produced were thereafter forged in air at about 980 C. and thereupon hot rolled into sheet of about 40 mil gauge at about 700 to 925 C.

Also in Tables I to V, inclusive, the alloys designated A were produced from high purity or iodide base titanium, obtained by the process set forth in the Van Arkel Patent No. 1,671,213; while those designated PA or RS were produced from titanium of commercial purity as obtained by the magnesium reduction of titanium tetrachloride in accordance with the patent to Kroll No. 2,205,854.

The beta transus temperature varies with the alloying constituents and content of each, and can be determined for any particular analysis by quenching specimens from the progressively higher temperatures and observing the microstructure. When the betal transus temperature is obtained, the specimen will quench to an all-beta microstructure, whereas on quenching from lower temperatures, some alpha phase will be present.

What is claimed is:

1. A method for producing a titanium-base alloy article having a relatively low yield strength and a relatively high ratio of ultimate tensile strength to yield strength, comprising heat-treating a titanium-base alloy consisting of at least one alpha stabilizer selected from the group consisting of 1 to aluminum, 1 to 23% tin, 1 to 19% antimony, and at least one beta stabilizer selected from the group consisting of 1 to 15% molybdenum, 2 to 20% vanadium, 1 to 8% manganese, 1 to 10% chromium and 1 to 5% iron to a temperature about that at which said alloy shows a minimum point on its yield strength, solution heat treating temperature curve, and rapidly quenching to produce a yield strength to ultimate tensile strength ratio of between 0.25 and 0.75.

2. A titanium-base alloy article produced in accordance with the method of claim 1.

3. A method for solution heat treating a thin section product composed of an alloy consisting essentially of aluminum in amount from about 1 to about 8%, a beta stabilizer selected from the group consisting of chromium in amount from about 2 to about 10%, iron in amount from about 2 to about 5%, vanadium in amount from about 2 to about 20%, molybdenum in amount from about 2 to about 15 and manganese in amount from about 2 to about 8%, and balance titanium with incidental impurities, which comprises heating said product for from about 15 minutes to about 2 hours at a temperature about that at which said alloy shows a minimum point on its yield strength, solution heat treating temperature curve, and rapidly quenching said product from said temperature thereby to provide as a characteristic thereof a yield strength to tensile strength ratio of between 0.25 to 0.75.

References Cited UNITED STATES PATENTS 2,554,031 5/1951 Jaifee et al -1755 2,575,962 11/1951 Jaffee et al 75-175.5 2,596,485 5/1952 Jaifee et a1 75-1755 2,675,309 4/1954 Vordahl 75-1755 2,726,954 12/1955 Jaffee et a1. 75-1755 2,777,768 1/1957 Busch et al. 75-1755 2,798,806 7/1957 Jatfee et a1 75175.5 2,880,087 3/1959 Iaffee et a1 75-1755 2,453,896 l1/1948 Dean 148-13 2,711,960 6/1955 Methe 75-1755 2,718,465 9/1955 Herres 75-1755 2,754,204 7/1956 Jafiee et a1.

2,864,697 12/1958 Busch et al.

FOREIGN PATENTS 718,822 3/1942 Germany.

679,705 9/ 1952 Great Britain.

CHARLES N. LOVELL, Primary Examiner. 

1. A METHOD FOR PRODUCING A TITANIUM-BASE ALLOY ARTICLE HAVING A RELATIVELY LOW YIELD STRENGTH AND A RELATIVELY HIGH RATIO OF ULTIMATE TENSILE STRENGTH TO YIELD STRENGTH, COMPRISING HEAT-TREATING A TITANIUM-BASE ALLOY CONSISTING OF AT LEAST ONE ALPHA STABILIZER SELECTED FROM THE GROUP CONSISTING OF 1 TO 10% ALUMINUM, 1 TO 23% TIN, 1 TO 19% ANTIMONY, AND AT LEAST ONE BETA STABILIZER SELECTED FROM THE GROUP CONSISTING OF 1 TO 15% MOLYBDENUM, 2 TO 20% VANADIUM, 1 TO 8% MANGANESE, 1 TO 10% CHROMIUM AND 1 TO 5% IRON TO A TEMPERATURE ABOUT THAT AT WHICH SAID ALLOY SHOWS A MINIMUM POINT ON ITS YIELD STRENGTH, SOLUTION HEAT TREATING TEMPERATURE CURVE, AND RAPIDLY QUENCHING TO PRODUCE A YIELD STRENGTH TO ULTIMATE TENSILE STRENGTH RATIO OF BETWEEN 0.25 AND 0.75. 